Tom,
I am cycling a Winston 100 a-hr bank at 0.41C for 2 hours, 4 times a day. In 18 months I should reach 2000 cycles at 82% DOD and will let the group know about cycle life. What I have found is these cells appear to be rated very conservatively, and the a-hr rating is given for a 1 C load to 80% DOD. Hence a 100 a-hr cell is really a 120 a-hr to 100% DOD.
I'm on cycle #189 as I type and past capacity tests have shown no loss.
Bob
From: "boat_works@yahoo.com" <boat_works@yahoo.com>
To: electricboats@yahoogroups.com
Sent: Monday, January 20, 2014 12:09 AM
Subject: [Electric Boats] Thoughts on lithium after 1000 hrs runtime
Hi All,
Today I had a nice 3 hour cruise in my launch which put the log over the 1000 hour mark. It took 44 months to get that many hours in.
It seemed like a good time to take stock of the theoretical potential lifespan of the battery bank. Sure, this is all based on the manufacturer's specs, but what else do we have to go on? This cell chemistry is still too new to have much real-world end-of-life info available. I can say that I have seen no degradation in cell performance.
These 180Ah CALB SE series cells are rated for 2000 cycles when discharged to 80% of capacity. So that would mean the total Ah available would be (180Ah)(.80)(2000) = 288,000Ah.
I have consumed 11,900Ah so far, which, if the specs reflect reality, is about 4% of the battery lifespan Ah. According to CALB, if I continue to use my boat as I have been, I have 85 years of operation left in these cells. Maybe I should put them in my will.
Well, we'll see...
And just to stretch the point, CALB claims that after those 288,000Ah, the cells aren't actually ready to be replaced, they still have 80% of their original capacity available.
And other manufacturers rate their cells at 3000 cycles if the depth of discharge is only 70%. I've never had to run mine below 35% SOC, since I bring along a generator if I think I might need it.
So I might not use these cells up in my lifetime, or my nephew's lifetime....
Or they might have some sort of calendar life that we haven't figured out yet. Or maybe the lab testing might not match what we experience in our boats.
Time will tell.
-Tom
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